The subject of the present invention is a guide and control device for an agricultural machine subjected in operation to a lateral thrust in relation to its direction of traction, especially a disk-type stubble-plough.
The machine is of the type comprising a frame equipped with blades, disks or shares, front and rear carrying wheels and with a furrow wheel, and the device comprises a system for controlling the wheels in order to change them from a road-travel position to a working position, and vice versa.
In conventional machines of this type, such as the stubble-ploughs described in French patents 2,536,239 and 2,525,857, front guidance is obtained by means of a single wheel under the control of a compensating bar of a tractor. The wheel, because it is thus subject to the lateral oscillations of a coupling drawbar during work, follows the directional movements determined by the travel of the tractor. Moreover, this wheel moves along on the bottom of the furrow dug by the last disk of the machine during the preceding pass, in a plane inclined in relation to the vertical plane. The purpose of this arrangement is to wedge the wheel in the furrow angle formed by the vertical wall cut out of the soil and the furrow bottom, in order to counteract the lateral thrust exerted by the action of the disks and thereby keep the machine guided in the path of movement of the tractor.
A suitable system makes it possible to keep the inclined wheel in the working position and in the vertical plane in the road-travel position of the machine, so as to prevent the tire of the wheel from wearing and being rolled off the rim, and in order to make the maneuvering of the wheel easier during road transport at a higher speed
This known guide device has several major disadvantages.
First of all, the connecting linkage between the front wheel and the compensating traction bar of the machine takes up a considerable amount of space, thus requiring a large steering-lock clearance. The position of the machine is therefore very far to the rear in relation to the tractor. This large bulk of the coupling arrangement gives rise to appreciable losses of cultivated areas in the bends at corners of the fields. Although this defect is of little importance on large areas of extensive cultivation, such as are found particularly in America or Australia, this waste makes the machine virtually useless on the plots of land of smaller area on European farms, where the entire area has to be cultivated, and above all when the machine travels along the edge of fences or hedges.
Another disadvantage of the known machines is that the change from the so-called working position of the wheels to their transport position, and vice versa, is relatively clumsy. In fact, this maneuver requires a lifting force at the front of the machine and an arduous rotation of the wheel shaft, usually by means of a spanner or a lever dangerous to handle or with the aid of a jack in the loose soil of a field. Finally, another disadvantage is the loss of guidance noticed whenever the wheels meet non-fixed obstacles, such as clods of hard earth, stones, wood, or fixed obstacles, such as rocks and roots.
The change of the rear carrying wheels from their road-travel position to their working position, and vice versa, is especially laborious, since the manoeuvre has to be repeated for each wheel and moreover completed by an additional manipulation of the furrow disk associated with one of the wheels.